High temperature insulating shape and method of manufacture



8 Patented Nov. 6, 1945 U] UL I IUIUI Ullw PATENT OFF-ICE HIGH TEMPERATURE INSULATING SHAPE AND DIETHOD OF MANUFACTURE Henry A. Kieselbach, Montclair, and Earl R. Williams, North Plainfield, N. 1., assignors to Johns-Manville Corporation, New York, N. Y., a corporation of New York No Drawing. Application December 15, 1942, Serial No. 469,122

3 Claims. (01. 92-54 The present invention relates to high temperature insulating blocks or shapes, and is particularly concerned with high temperature insulatin shapes incorporating diatomaceous silica as a major ingredient.

The high-temperature insulating shape and method of manufacturing same, which form the subject of the present invention, represent improvements on the Heat insulating composition and method of making which is described in U. S. 10

Patent #2,033,106 granted March 3, 1936 to Arthur B, Cummins. Insulating blocks of the type described in the Cummins patent develop considerable shrinkage during the period of manufacture and cannot therefore be molded to precise dimensions; so that such blocks must be molded and thereafter planed down to desired dimensions for use. The manufacture of finished blocks by such method is therefore costly and time-consuming,

and involves considerable loss ofmaterial in the form of trimming waste.

A primary object of the present invention is to provide an improved method of manufacturing high temperature insulating shapes incorporating diatomaceous silica as a principal ingredient 1 o PI'EO n ens 11s, in a g 511 fid wasteful planing and trimming operations. A more particular object of the present inven- 11 is to provide a precision molded heat-insulat- 1118 Shape pted for use at elevated temperatures 0 3 in the neighborhood of 2000 F. and having improved strength and insulation capacity at such elevated temperatures and also at normal temperatures. 3-

With the above and other objects and features a;

in view, the invention consists in the improved high temperature insulation shape and method of manufacture hereinafter described and more particularly defined in the appended claims. 40 The insulation shape which forms the subject i of the present invention incorporates diatomace ous silica as a principal ingredient. Thulatomaceous silica is preferably subjected to a prelim- H ca ;an arela veysma I amount of a s ate may be added prior to calcination.

The high temperature insulating blocks herein described differ primarily from the blocks described in the aforementioned Cummins patent 5 in that the principal bonding agent whicli is used in their manufacture by the present invention comprises self-setting normal magnesium carbonate, rather than pre-formed basic magnesium carbonate? uitable flux such as sodium carbontion is based on the obser- 5i be ast to precise Q ensions and cured as rogg pro c providing the. e casting or molding l nsarecarredou un ers a controlled ggggimggs empera ure an supe atmospheric pressure. or mo mg the preersennnemsfifs'a'mtamme a men proportion of diatomaceous silica, it is essential that the molding and curing operations be carried out in molds having pervious walls and under moderate superatmospheric pressures. It is also desirable to incorporate in the composition a small amount of bentonite as an additional bonding agent which improves the strength of the block, particularly at high temperatures, apparently by reaction in situ with the silica to form a strong silicate at temperatures in the neighborhood of 2000 F.

In the manufacture of heat insulating shapes in 4 accordance with the present invention, the following illustrative method may be practiced: in

case bentonite is used as one of the bondin components of Hie mix" tfil'eit, is Hist thorough l'y hyan aqueous suspension of finely-divided normal ay adfi E SllS- on o fine -i d rate ma esia un-' de'r conditi uce normal magnesium car"- Sonate (MQCOa-3Hz0) directly, or else a solution e um icarbonate may be heated under conditions to produce the normal carbonate. Asbestos fibres and calcined diatomaceous silica may be added to the hydrated magnesia or bicarbonate before the treatment converting it to normal carbonate, or the asbestos and diatomaceous silica may be added after formation of the normal carbonate suspension. After suitable hydration of the bentonite, and at 1- formation of the aqueous carbonate suspensio ry may then be dewatered or adjust to :mlmgenmmfis cy. In preparing e manesium carbonate slurry the treatment should be such as to convert at least a substantial o r- I c ITaktHI i J UJ-Ni of the slurry to a suitable concentration, which may be approximately if/fit 'pyTreight-of. solids,

WIIIIII 11C suspension c 1 '4- n t c I c oowmg the step of adjusting the consistency 2 p I 2,388,549 Y the slurry is introduced under a pressure of 10 to 25 lbs. into a pressure filter mold which is dimensioned to'produce a block of the desired shape and which is provided with perforated walls to allowctor drainage of water from the mold. A suitable mold, "for example; maybe one'dimensioned to produce a block 36 inches by 6 inches by 2 inches (36" x 6" x 2"). The mold should is then removed from the mold and subsequent completion of the setting operation is effected in the usual air-drying oven at a temperature of p 'liliev-followinguormulae illustrate various com-,

positions bf molding mixtures *for hightemperature insulating blocks having particularly desirabie properties in accordance with this invention:

' sPcrcenl Percent Percent Percent Percent gsbesto'sfibl'e 12 enwnlze.-.-....-..- i c 5 3 Normal nln'ilnaoiuln n ate crystals 60 Calcineddiatomaoeouaaihca" "i... a 72 63 35 38 Natural mtommtilicasu rs after molding slurries of the compositions given 20 in Formulas I-V above, under a molding and dewaterlng pressure of 20 lbs. gaugeydurlng which 'arslurry *of approxmately-4 %solids concentration is dewatered to an acceptable consistency df approximately 30% solids concentration; and

25 after curing the mold charges by direct applica- 'tion thereto pf steam under 5 lbs. pressure tor a period of a'bout5 minutes to effect a preliminary set followedby final cure in-a'drying oven, insula ting blocks -of the following characteristics one which can be mounted in afilt'er'iiressfrai'ne resulted:

Q Formula Formula Formulal Formula Formula '1 "-11 HI IV V and in winch the perrcrateu'n olu'siue'walls either form, or abut'on, 'a'perfor'ated'side ora'urainage and steam jacket. with drainage m1 "steam Jackets thus located on 'each'slue of the 'mrild'and provided "with suitable water btitlts and steam inlets, it is pb's'sibletb enect "rapid ura'inage (if water from the mold 'chare'e under hydrostatic -or pump pressureniaintsmed xmtne'slurry hurin'g the pe'riod 'of'cliar'g'iiig the mold and 0T dewatering 'the charge; andtofherealfter use such steam T j acke'ts for "introduction 'o'f -hot steamiinto direct contact with fthe mold charge during the subsequent curing operation wherein the mold charge is cured by heating to convert the normal magnesium carbonate to basic magnesium carbonate. A H i 7 After the mold has been completely charged with asuiteblyiproportioned mixtureof diatomaceous silica, bentonite, self-setting magnesium carbonate and asbestos, valves #in the slurry charging -.-pipes are-closed and the :mold charge is immediately cured, or'at least :par-tiallycured, by application -01 a eontrolled degree -of heat to the mold charge while "still within the mold.

During the 'curing operation steam 'or hot water at asuitable curing itemperaturenind underi pressure approximating 5 lbs. :gauge, is introduced into direct contact with will sides of the 'unoltl, -or at least ln'to with those riches of the mold wall area which are 'periorated. The rstemn *or Water thus supplied uunctionszas 'n'source Of curlng 'heat and also 91s a'qluifi nesweonveymg medium for transferring tlieheat mough the mold charge. "In this way the necessary ameunt of preliminary set is mparted to the me'la charge or block nnder' cure'within a comparatively brief period 01' 5-15 minutes. The cast block or shape Insulation blocks or *s'hapes'thus made formulas incorporating approximately 12% as-- 40 bestos fibre and in which themajor constituents are 'diatoma'ceous silica (natural or calcined) and'basic magnesium carbonateiormed in situ from normal seli 'setting magnesium carbonate, exhibit no measurable shrinkage'in'yohime'dun- -ing the molding, cur-mg and drying operations.

Consequently, the 'blocks can be precision molded to iprecme dimensions, and require nu machining, planing 'or finishing, ;except possibly for a small amoimt'ortrinimingon that ifaceor edge "Heat-insulating 'liloks which have been made "in accordance with the indicated formulas are non-shrinking attne molding and curing tem- .peratures, and they also exhibit high resistance -to-shrinkage orrtailure at elevated temperatures approximating 2170b Products made vfroin J stantially -dust-drone; -and -the resulting blocks have a lower-densityanda hig'herrat'iont modulusbf rupture =to'density than'any similar high temperature insulation blocks 01 comparable oomposition heretofore made. -Blocks made 4n 7 accordance with the present invention havela atrength modulus-density 'ratio of at rleast 3 throughout -a density from 1 16-23 lbs. per cubic-"root. a '51:;

mar ito its incorporation with thew wingredients of the block, the diatomaceous earth for "the block 'rormed au'iacent the slurr 'ch'a'rgr a ink inle'tof the mold.

What we claim is:

with novelty over the prior art.

1. A method of manufacturing a heat insula- 15 tion block adapted for use at elevated temperaes mmpfi aform wm 4 -7 /2 olids concentr ion consisting of a weight of finely divided diatomas nesium car onate an m1 oni e and asbes fibers, introducing a. charge of the slurry under pressure into a filtering mold, partially dewatering and shaping the charge while completing the charging operation, and 25 curing the block while confined within the mold by circulating an aqueous heating fluid under low pressure in direct contact with the mold walls and mold charge to convert the normal magnesium carbonate to basic magnesium carbonate.

2. A filter molded and cured heat insulation (Ifoss Reference block retaining the mold dimensions and which exhibits very small shrinkage in use at high temperatures, consisting essentially of calcined finely divided diatomaceous silica in amounts representing 35%-'72% by weight of the block and approximately 12% asbestos fibers integrally bonded with 3%6% bentonlte and 10%-50% basic magnesium carbona formed in situ by decomposition of self-setting normal magnesium carbonate, said block having a dry density or 17-23 lbs. per cubic ft. and having a transverse strength exceeding 80 lbs. per square inch.

3. A method of manufacturing a heat insulation block adapted for use at elevated temperatures comprising, forming an aqueous slurry of 4 -7 solids concentration comprising 35-72% dry weight of finely divided diatomaceous silica, 10-50% finel divided normal magnesium carbonate, and minor proportions of bentoni-te and asbestos fibers, pressure filter molding a measured charge of said slurry, partially dewatering and shaping the slurry solids to form a block while completing the molding operation, partially curing the block while confined within the mold by maintaining an aqueous heating fluid in direct contact with outer surfaces thereof to convert the normal magnesium carbonate to basic magnesium carbonate, and drying the thus cured block.

HENRY A. KIESELBACH. EARL R. WILLIAMS.

Examine: 

